Codemod

Codemod (opens new window) is a tool/library developed by FaceBook to assist you with large-scale codebase refactors that can be partially automated but still require human oversight and occasional intervention. Code refactoring (opens new window) is the process of restructuring existing computer code—changing the factoring—without changing its external behavior.

Example: Let's say you're deprecating your use of the <font> tag. From the command line, you might make progress by running:

codemod -m -d /home/jrosenstein/www --extensions php,html \
    '<font *color="?(.*?)"?>(.*?)</font>' \
    '<span style="color: \1;">\2</span>'

For each match of the regex, you'll be shown a colored diff, and asked if you want to accept the change (the replacement of the <font> tag with a <span> tag), reject it, or edit the line in question in your $EDITOR of choice.

Codemods are scripts used to rewrite other scripts. Think of them as a find and replace functionality that can read and write code. You can use them to

1. update source code to fit a team’s coding conventions,
2. make widespread changes when an API is modified, or
3. even auto-fix existing code when your public package makes a breaking change.
4. ...